Process for aromatic substitution

ABSTRACT

Substituted aromatic derivatives are prepared by reacting an aromatic compound with a Group VIII platinum metal salt wherein the substituent introduced is derived from the anion portion of said Group VIII platinum metal salt.

United States Patent [191 Robinson 1 Apr. 3, 1973 [54] PROCESS FORAROMATIC [51 Int. Cl ..C07c 69/14 SUBSTITUTION [58] Field of Search..260/479 R [75] Inventor: Robert E. Robinson, Columbia, SC. ReferencesCited [73] Assignee: National Distillers and Chemical Corporation, NewYork, N.Y. UNITED STATES PATENTS 22 Filed; Jam 25 1971 3,493,605 2/1970Selwitz ..260/488 [21] APPL N03 109'628 I Primary Examiner-James A.Patten Related U.S. Application Data U.S. Cl. ..260/479 R Attorney-AllenA. Meyer, Jr.

[57] ABSTRACT Substituted aromatic derivatives are prepared by reactingan aromatic compound with a Group VIII platinum metal salt wherein thesubstituent introduced is derived from the anion portion of said GroupVIII platinum metal salt.

6 Claims, No Drawings PROCESS FOR AROMATIC SUBSTITUTION This applicationis a division of application Ser. No. 809,406, filed Mar. 21, 1969, (nowUS. Pat. No. 3,578,716) which is a continuation-in-part of applicationSer. No. 631,917, filed Apr. 19, 1967 and now abandoned, which in turnis a continuation-in-part of applications Ser. No. 282,559 (filed/23/63) now abandoned, Ser. No. 282,594 (filed 5/23/63) now abandoned,and Ser. No. 282,595 (filed 5/23/63) now abandoned.

The present invention relates to a novel reaction of aromatic compounds.More particularly, it pertains to a novel process for preparingsubstituted aromatic derivatives, and particularly monochlorobenzene, bythe reaction of an aromatic compound with a Group VIII platinum metalsalt.

Monochlorobenzene is in demand commercially in large volume as anintermediate in the synthesis of phenol, aniline, DDT[1,1,l-trichloro-2,2-bis(pchlorophenyl)ethane], and other products.

One approach to synthesizing monochlorobenzene has involved the reactionof benzene with a metal halide. An article by Kharasch et al. J. Am.Chem. Soc., 53, 3053 (1931), describes the chlorination of benzene inliquid phase at atmospheric pressure using auric chloride as thechlorinating agent. The reaction requires dry, thiophene-free benzeneand anhydrous auric chloride. The presence of ether, acetic acid,alcohol, ethyl acetate, and other reagents containing oxygen preventsthe reaction from taking place. Further, if the benzene is added to theauric chloride, only polysubstituted chlorobenzenes are produced.Regeneration of auric chloride from the precipitated aurous chlorideformed in the reaction by treatment with chlorine gas is suggested as ameans of making the reaction catalytic with respect to the gold salt.Such regeneration cannot be performed in situ if further chlorination ofthe benzene is to be avoided.

In a recent series of articles by Kovacic and coworkers, the directreaction of ferric chloride with benzene and various substitutedbenzenes in anhydrous liquid phase reaction is explored. With alkyl andhalo substituted benzenes, various isomeric mixtures are obtained. Withbenzene, the products comprise a small amount of chlorobenzene (no morethan 6% yield) and a water-insoluble black solid. Chlorination fails tooccur when AlCl SnCl and CuCl are substituted as chlorinating agents forchlorobenzene in place of FeCl;,.

Accordingly, it is one object of this invention to convert benzene tomonochlorobenzene by a more direct and more efficient process than ispossible by prior art processes.

A further object of this invention is to provide a novel and effectiveprocess for the preparation of substituted aromatic compounds.

Another object of this invention is to provide a vapor phase process forintroducing substituents onto the aromatic ring of aromatic compounds.

Further objects of this invention will become apparent from thefollowing description and embodiments.

In accordance with this invention, substituted aromatic compounds areproduced directly and effectively by reacting an aromatic compound witha Group VIII platinum metal salt.

The starting aromatic compound may be an aromatic hydrocarbon, e.g.,benzene, naphthalene, anthracene, phenanthrene, toluene, p-xylene, ethylbenzene, and biphenyl; a phenol, e.g., phenol, catechol, resorcinol,hydroquinone, pyrogallol, m-cresol, picric acid, and alpha-naphthol; anaromatic alcohol, e.g., benzyl alcohol, cinnamyl alcohol,andtriphenylcarbinol; an aromatic amine, e.g., aniline, o-toluidine,m-phenylenediamine, anthranilic acid, and alphanaphthylamine; anaromatic ketone, e.g.,

benzophenone, acetophenone, phenylacetone, and alpha-chloroacetophenone;an aromatic nitro compound, e.g., nitrobenzene, m-dinitrobenzene,alphanitronaphthalene, and beta-nitroanthracene; an aromatic halide,e.g., fluorobenzene, chlorobenzene, bromobenzene, iodobenzene,m-dichlorobenzene, alpha-chloronaphthalene, and p-chlorotoluene; anarylsulfonic acid, e.g., benzenesulfonic acid, ptoluenesulfonic acid,sulfanilic acid, and alphanaphthalenesulfonic acid; an arylcarboxylicacid, e.g., benzoic acid, phenyl acetic acid, cinnamic acid,paminobenzoic acid, o-toluic acid, terephthalic acid, alpha-naphthoicacid, and alpha-anthroic acid; an aromatic anhydride, e.g., phthalicanhydride, benzoic anhydride, and acetic benzoic anhydride; an aromaticether, e.g., diphenyl ether, anisole, phenetole, anisaldehyde, andguiacol; an aromatic aldehyde, e.g., benzaldehyde, salicylaldehyde,cinnamaldehyde, and piperonal; a quinone, e.g., p-quinone,alphanaphthoquinone, and anthraquinone; an aryl mercaptan, e.g., phenylmercaptan, benzyl mercaptan, p-tolyl mercaptan, and biphenyl mercaptan;an aromatic amide, e.g., benzamide, phthalamide, phenylacetamide, andtoluamide; an aromatic nitrile, e.g., benzonitrile, o-tolunitrile,phenylacetonitrile, and cinnamonitrile; as well as mixtures of two ormore of the above compounds or types of compounds. Heterocycliccompounds, e.g., pyridine, thiophene, and quinoline, may also serve asthe starting aromatic compound. I

The platinum metal portion of the Group VIII metal salt may bepalladium, platinum, ruthenium, rhodium, osmium or iridium. The anionportion may include a halide, e.g., fluoride, bromide, chloride, oriodide; a cyanide; a carboxylate such as acetate, propionate, benzoate,etc.; a cyanate; an alkoxide, such as methoxide or ethoxide; or anaromatic oxide, such as phenoxide or naphthoxide. Examples of Group VIIIplatinum metal salts suitable for the practice of this invention includepalladous chloride, palladous bromide, platinous chloride, rhodiumtrichloride, palladous fluoride, palladous iodide, potassiumchloropalladite, platinous bromide, platinous iodide, platinic bromide,ruthenium dichloride, ruthenium trichloride, osium dichloride, osmiumtrichloride, osmium tetrachloride, iridium trichloride, iridiumtetrachloride, iridium tribromide, iridium tetrabromide, palladousacetate, palladous cyanide, palladium benzoate, palladous cyanate,palladous methoxide, palladous ethoxide, palladous phenoxide, and thelike.

The Group VIII platinum metal component may be employed unsupported orsupported on a suitable material, such as carbon, silica, alumina, orthe like. The supported catalysts may be obtained commercially or may beprepared by any convenient means, such as by dissolving the metal saltor salts in a suitable solvent,

e.g., water; adding the support, e.g., carbon; and evaporating thesolvent with heat under vacuum. Only catalytic amounts need be employed,and specific amounts may vary from about 0.05 up to about percent byweight, based on the total reaction mixture, with the preferred amountbeing within the range of about 0.2 to about 5 percent by weight.

The process of this invention may be carried out with the aromaticcompound in either liquid or gas phase. To carry out the process withthe aromatic compound in liquid phase, the reactants are charged to asuitable reactor, such as a conventional stirred reactor or an agitatedpressure tube reactor, and thereafter agitated for a period of time at asuitable temperature, after which the product, which is a substitutedaromatic compound or compounds, may be separated by conventional means,e.g., fractional distillation, decantation, filtration, etc. Thearomatic compound may serve as the reaction medium, in which case it maybe maintained in substantial excess of that required to react with theGroup VIII platinum metal salt. Alternatively, an inert diluent may beadded and,'if desired, serve as the bulk of the reaction medium. Suchinert diluents must be nonreactive with respect to the Group VIIIplatinum metal salt and the aromatic compound and must exert at leastsome solvent action thereon at the reaction temperature. Suitablediluents include water; acetic acid; aliphatic hydrocarbons, e.g.,hexane, heptane, cyclohexane, and isopentane; other aliphatic compounds,e.g., dimethylformamide, butyl chloride, methanol, ethanol, dimethylsulfoxide, acetonitrile, chloroform, carbon tetrachloride, and carbondisulfide; etc. It is preferred to use as the reaction medium a mixtureof an excess of the aromatic compound undergoing reaction and water.

In carrying out the reaction satisfactorily, that the presence of anacid acceptor is not required and is, in fact, to be avoided. Thus, itis unnecessary to include acid acceptor materials or buffering agentscapable of binding free acid present in the reaction mixture.

The course of the reaction is independent of the reaction pressure, theonly requirement being that the pressure on the reaction mixture-be suchthat at least a portion of the aromatic compound is maintained inliquidphase. Generally, the reaction is carried out under the autogenouspressure generated by the components of the reaction mixture. Inpractice, these pressures will range from about 1 atmosphere up to 100atmospheres or more.

To carry out the process of this invention with the aromatic compound ingas phase, the aromatic compound is volatilized prior to its contactwith the Group VIII platinum metal salt and subsequently contacted withthe Group VIII platinum metal salt in a conventional manner and inconventional apparatus. For example, the Group VIII platinum metal saltmay be placed in a tubular reactor and the aromatic compound in gaseousform passed or circulated through the reactor. The product, which is asubstituted aromatic compound or compounds, may be recovered byconventional means from the exhaust gases. If desired, the Group VIIIplatinum metal salt may be supported on a suitable material, such ascarbon, carbonate, silica, alumina, or the like. The supported salt maybe obtained commercially or may be prepared by any convenient means,such as by dissolving the salt in a suitable solvent, e.g., water;adding the support, e.g., carbon; and evaporating the solvent with heatunder vacuum.

The gas phase reaction generally is carried out at a 5 pressure betweenabout 0.25 to 250 atmospheres and preferably between about 1 and 100atmospheres.

In one specific embodiment of the present invention, a gaseous streamcomprising benzene and, if desired, a carrier gas is passed overpalladous chloride, and the chlorobenzenes obtained as the product arerecovered from the exhaust gases. A constant level of benzene in the gasstream may be maintained conveniently by saturating a carrier gas withbenzene by passing it over or through liquid benzene and thereafterthrough the reactor. It is possible also, if desired, to vaporize thebenzene separately in a flash chamber and to meter it in separately. Theexhaust gases are cooled and scrubbed for the recovery of thechlorobenzenes. Thus the product, chlorobenzenes, is obtained insolution with excess benzene, if any, and this mixture may be separatedby any convenient means, e.g., by fractional distillation.

The reaction between the Group VIII platinum metal salt and the aromaticcompound to produce substituted aromatic compounds takes place betweenabout and 600C. Preferably, however, the reaction when run in liquidphase is carried out at a temperature between about 100 and 300C. andwhen run in vapor phase at a temperature between about 300 and 500C.

The substituted aromatic compounds produced by the process of thisinvention are of two types: (1) a derivative of the starting aromaticcompound containing as an additional substituent on an aromatic ring ananion portion of the Group VIII platinum metal salt and (2) a derivativeof the starting aromatic compound containing as an additionalsubstituent on an aromatic ring a duplicate of the starting compoundless one hydrogen atom, that is, a dimer of the starting aromaticcompound less two hydrogen atoms at the point of bonding. The first typeof product can be obtained from the reaction of a halide of a Group VIIIplatinum metal, e.g., palladium chloride, and anaromatic compound, e.g.,benzene, which produces an aromatic halide, e.g., chlorobenzene.Similarly, palladium chloride can be employed to convert chlorobenzeneto o-, m-, and p-dichlorobenzene; nitrobenzene to an isomeric mixture ofchloronitrobenzenes; aniline to chloroanilines; naphthalene to alphaandbetachloronaphthalene; anthracene to 9-chloroanthracene; and so on. Thesame reactions can be carried out by using other Group'VIII platinummetal chlorides such as rhodium trichloride, platinum chloride, iridiumchloride, or ruthenium chloride. In a like manner, by selecting GroupVIII- platinum metal salts containing other anions, e.g., palladouscyanide, palladous acetate, palladous methoxide, platinous phenoxide,palladous cyanate, and iridium tribromide, benzene can be converted to.benzonitrile, phenyl acetate, anisole, diphenyl ether, phenylisocyanate, and bromobenzene, respectively.

The second type of product can be obtained as a coproduct of thereactions described above. For example, under certain conditions thereaction between palladium chloride and benzene, in addition toproducing chlorobenzene, produces at least some biphenyl, the

dimer of the starting compound. Production of this byproduct appears todepend upon reaction temperature. For example, at 150C. the productmixture from the reaction of palladous chloride with an excess of liquidbenzene contains about 85 mole percent of biphenyl and mole percent ofmonochlorobenzene. At 250C. and above, however, monochlorobenzene isproduced from the same reaction mixture to the substantial exclusion ofbiphenyl. Similarly, below about 250C. the reaction between palladouschloride and toluene leads to an isomeric mixture of monochlorotoluenes,i.e., 0-, m-, and p-chlorotoluene, and 4,4-dimethylbiphenyl and isomersthereof. In a like manner it is possible to react palladium chloride orother Group VIII platinum metal salts with chlorobenzene to produce anisomeric mixture of dichlorobenzenes and dichlorobiphenyls, including amajor proportion of 4,4'-, 3,3'-, and 3,4- dichlorobiphenyl and a minorproportion of 2,4-, and 2,3'-, and 2,2'-dichlorobiphenyl. Correspondingisomeric mixtures are produced from aniline, nitrobenzene, benzonitrile,phenyl acetate, etc. From naphthalene the products include, in additionto isomeric chloronaphthalenes, a mixture of 1,1 1,2'-, and 2,2-binaphthyl.

Generally, the molar ratio of aromatic compound to the Group VIIIplatinum metal salt used as a starting material ranges from about 0.3 to10.

A convenient source of the anion being introduced is a protonated formof said anion, e.g., hydrogen halides such as hydrogen chloride andhydrogen bromide for chloride and bromide ions, acetic acid for acetateion, cyanic acid for cyanate ion, etc.

If desired, the product chlorobenzene may be passed over appropriatehydrolysis catalysts by methods known to the art and converted to phenoland hydrogen chloride. The hydrogen chloride may then be used in asubsequent chlorobenzene synthesis, thus providing an overall processfor phenol from benzene and oxygen:

With respect to the production of monochlorobenzene, the present processexhibits several distinct advantages over the processes of the art. Itgives a high conversion of benzene to monochlorobenzene with only asmall amount of dichlorobenzene being formed, and, moreover, hydrogenchloride can be used as the source of chlorine. For example, conversionsof over 70 weight percent of benzene to chlorinated benzenes, of whichabout 90 weight percent is monochlorobenzene, can be realized by thisprocess. Another advantage of this process is the ability of thereaction medium to tolerate water. This feature eliminates the need ofanhydrous reactants and simplifies the separation of the water-insolubleproducts from water-soluble catalyst components.

Both the liquid and the gas phase embodiments of the present processexhibit distinct advantages over the art. For example, by means of thepresent process it is possible to obtain monochlorobenzene with littleor no simultaneous production of polychlorobenzenes. In the liquid phaseembodiment, the reaction medium can tolerate water, thereby eliminatingthe need of anhydrous reactants and simplifying the separation ofwater-insoluble products from water-soluble catalyst components. The gasphase embodiment enables the process to utilize in the synthesis ofchlorobenzene and other aromatic products the advantages normallyattendant with vapor phase techniques, e.g., simple equipment, readyhandling at elevated temperatures, convenient recycle, and the like.

The products obtainable by the present process, such as chlorobenzene,chlorotoluene, chloronitrobenzene, dichlorobenzene, benzonitrile, phenylacetate, biphenyl, polyphenyls, and the like, find widespread commercialuse as chemical intermediates in the synthesis of polymers, copolymers,dyes, insecticides, and the like.

EXAMPLE I EXAMPLE II By the procedure of Example I, 0.13 gram (0.71millimole) of palladous chloride, 0.3 ml. of benzene, and 0.3 ml. ofwater were heated at 150C. for 18 hours. Analysis by vapor phasechromatography indicated the presence of chlorobenzene and biphenyl in amolar ratio of about 1:8 and in a yield of 40.3 percent and 5 percent byweight, respectively.

EXAMPLE III EXAMPLE IV By the procedure of Example I, 0.18 gram (1.0millimole) of palladous chloride and 0.6 ml. of benzene were heated 30minutes at 250C. Analysis by vapor phase chromatography indicated thepresence of chlorobenzene and biphenyl and in a yield of 2.7 per-' centand 6.8 percent by weight, respectively.

EXAMPLE V By the procedure of Example I, 0.04 gram of palladouschloride, 0.3 ml. of nitrobenzene, and 0.3 ml. of water were heated 17hours at C. Analysis of the organic phase by vapor phase chromatographyrevealed the presence of materials whose retention times were identicalto those of chloronitrobenzenes.

EXAMPLE VI By the procedure of Example I, 0.04 gram of palladouschloride, 0.3 ml. of toluene, and 0.3 ml. of water were heated at 145C.for 18 hours. Analysis of the organic phase by vapor phasechromatography revealed the presence of materials whose retention timescorresponded to the monochlorotoluenes and the dimethylbiphenyls.

EXAMPLE VII By the procedure of Example I, 0.04 gram of palladouschloride, 0.3 gram of phenol, and 0.3 ml. of water were heated 2 hoursat 250C. Analysis of the organic phase by vapor phase chromatographyindicated the presence of mixed monochlorophenols.

EXAMPLE VIII By the procedure of Example I, 0.04 gram of palladouschloride, 0.3 ml. of chlorobenzene, and 0.3 ml. of water were heated 2hours at 250C. Analysis of the organic phase by vapor phasechromatography indicated the presence of o-, m-, and p-dichlorobenzenein the molar ratio :45:40.

EXAMPLE IX By the procedure of Example I, 0.1 1 gram (0.54 millimole) ofrhodium trichloride, 0.3 ml. of benzene, and 0.3 ml. of water wereheated 30 minutes at 250C. Analysis by vapor phase chromatographyindicated the presence of chlorobenzene. The yield was 1.5 percent byweight.

EXAMPLE X By the procedure of Example I, 0.091 gram (0.34 millimole) OFpotassium chloroplatinite, 0.3 ml. of benzene, and 0.3 ml. of water wereheated 30 minutes at 250C. Analysis by vapor phase chromatographyindicated the presence of chlorobenzene.

EXAMPLE XI EXAMPLE XII By the procedure of Example I, 0.04 gram ofpalladous cyanide, 0.3 ml. of benzene, and 0.3 ml. of water were heated60 hours at 150C. The presence of benzonitrile was detected bycharacteristic retention time on vapor phase chromatographic analysisand by hydrolysis of the residue (after evaporation of the benzene) tobenzoic acid. The benzoic acid was identified by mixed melting pointwith a sample of pure benzoic acid.

EXAMPLE xm By the procedure of Example I, 0.1 gram of palladous acetateand 0.3 ml. of benzene were heated for 2 hours at 250C. Analysis of theorganic phase by vapor phase chromatography indicated phenyI acetate(identified in the presence of the reaction mixture by correct retentiontime in three different vapor phase chromatographic columns) andbiphenyl.

EXAMPLE XIV Ten grams of 12 X 40 mesh carbon was impregnated withpalladous chloride by dissolving the palladium salt in water, adding thecarbon, and slowly evaporating the water in a rotating flask with heatand vacuum. The resulting material was packed in a glass tube and heatedto 325C. A stream of nitrogen saturated with benzene at room temperaturewas passed through the heated tube. Chlorobenzene was found in theeffluent stream by vapor phase chromatographic analysis.

While there are above disclosed but a limited number of embodiments ofthe process of the invention herein presented, it is possible to producestill other embodiments without departing from the inventive conceptherein disclosed. It is desired, therefore, that only such limitationsbe imposed on the appended claims as are stated therein.

What is claimed is:

l. A process for introducing a substituent onto an aromatic ring whichconsists in reacting an aromatic compound selected from the groupconsisting of benzene, nitrobenzene, toluene, phenol, chlorobenzene andbiphenyl, in vapor phase with a Group VIII platinum metal carboxylate ata temperature in the range of about 20C. to 600C. and at a pressure inthe range of about 0.25 and 250 atmospheres to produce a substitutedaromatic compound wherein the substituent introduced is derived from thegroup consisting of the anion portion of said Group VIII platinum metalcarboxylate and the aromatic compound, said Group VIII platinum metalcarboxylate being selected from the group consisting of palladium,platinum, ruthenium, rhodium, osmium and iridium acetate, propionate andbenzoate.

2. The process of claim 1 wherein the temperature is in the range ofabout 300 and 500C.

3. The process of claim 1 wherein the temperature is in the range ofabout to 300C.

4. The process of claim 1 wherein the Group VIII platinum metalcarboxylate is a palladium metal carboxylate.

5. The process of claim I wherein the Group VIII platinum metalcarboxylate is a platinum metal carboxylate.

6. The process of claim 1 wherein the aromatic compound is benzene.

2. The process of claim 1 wherein the temperature is in the range ofabout 300* and 500*C.
 3. The process of claim 1 wherein the temperatureis in the range of about 100* to 300*C.
 4. The process of claim 1wherein the Group VIII platinum metal carboxylate is a palladium metalcarboxylate.
 5. The process of claim 1 wherein the Group VIII platinummetal carboxylate is a platinum metal carboxylate.
 6. The process ofclaim 1 wherein the aromatic compound is benzene.